A new bioassessment multimetric index (BECOME) and diagnostic tool (BECOMEd) for small standing waters

Abstract

Small shallow lakes and ponds (SSWs) have high conservation value and support numerous ecosystem services. However, these small ecosystems face many threats, including eutrophication and internal biotic pressures like Cyprinidae or exotic bioturbators crayfish, which tend to shift biodiverse SSWs to a turbid state dominated by phytoplankton unfitted to numerous usages, and compromise the effectiveness of their restoration. The ecological quality of SSWs and the efficiency of their management still remain poorly evaluated because of the lack of adapted tools. To fill this gap, we propose a new multimetric index (BECOME) and a diagnostic tool (BECOMEd) both based on macrophyte and invertebrate communities. BECOME exhibits a high sensitivity to the impact of surrounding crops, urbanization and fertilized meadows, morphological alterations, and various internal biotic sources of alterations, in a wide variety of geological and climatic contexts. BECOME is especially innovative, because taking into account internal biotic sources of pressures neglected by most of the existing biological WFD-compliant indices for European lakes and ponds, despite their importance in SSW threats. BECOMEd allows to identify the major alteration sources and estimates their relative contribution to SSW degradation, helping managers to prioritize actions or to evaluate their effectiveness. The statistical design applied for the index construction has been fitted to develop biological index for ecosystems influenced by a wide amplitude of numerous environmental conditions. This design could be easily applied elsewhere in the world, for SSWs but also for other types of ecosystems.